North America Nebula - Gulf crop

[Bob Andersson]

Hi folks,

My astrophotography goal for the summer is a four panel mosaic of the North America nebula. I've previously taken an ultra-widefield image of the region using my 165mm f/2.8 Pentax medium format lens (this thread) but there's much more detail to be had with the 980mm focal length of my TEC 140. The only problem, of course, is that imaging at f/7 needs a lot more patience. Today I thought I'd see if the 16 unguided Hα subs I've captured so far, each of 1,000 seconds exposure time, would be enough to get the depth I wanted and here's the result of part of the image at 50% scale (you can click the image for a 100% crop factor version which also shows fainter stars):

No red, green or blue subs yet but they are planned for the future to add star colour. I'm still trying to refine my processing skills being pretty new to the game so for the first time I tried blending differently processed versions of the nebulosity. I blended a "No Stars" clone of the image with a copy of that "No Stars" image which had been HDRMultiscaleTransform-ed courtesy of PixInsight. The result was coloured (that will need more fine tuning - Hα colour and intensity always seems to be a difficult step to get right!) and then a "Stars Only" clone, which had also passed through PixInsight for a spot of deconvolution, was added back.

As I say, just a test image to find out if about four and a half hours of exposure time gives me the depth I want. The good news is "Yes, it does", the bad news for me is that I'm going to have to retake about half of the subs as the earlier images were taken with the camera rotated about 7°, enough to mess up the joins of the mosaic panels. Oh well, it keeps me out of the pub and reminds me how meticulous attention to detail isn't optional for astrophotography. At least I now know that the telescope, mounting and camera will eventually reward all the time spent over the coming months!

Bob.

[angusb1]

I've just been comparing this version to the same section of your previous one with the 165mm lens and the difference is pretty noticeable. The 165mm version is fantastic but this has more detail. Its very sharp indeed, and I can't wait to see the whole mosaic.

Are you planning to add any OIII?

[Gina]

Looking brilliant so far

[nmoushon]

This shows amazing detail! Great job. Though the stars look a bit odd..can't put my finger on it but somethings a bit off to my eyes...or maybe it my crappy screen at work idk. But can't wait to see what you get at the end of the summer!

[Bob Andersson]

.

I think I may have overdone the deconvolution - sharp round stars aren't what we expect to see. Or maybe it's because they are completely white. Live and learn!

Bob.

[Quatermass]

Looking very nice indeed.

[Uranium235]

I was going to say that 1000s unguided is impossible (for 99.5% of amateurs), but having just looked up your mount - I can see why you get such results.

Good detail on the nebula, you just need to be a bit less harsh on the stars

[Kbramley]

Superb start, I will be watching this with interest as I'm just starting a mosaic of this target myself, only with a modified DSLR and without narrowband filters.

Keith

[MikeD]

Excellent detail and contrast.

The neb is a little too smooth for my taste which IMO gives the image an unnatural feel, but l that's just my personal prefrence.

Having done this area myself as a nine frame Ha mosaic My hat goes off to you for going for a full colour mosaic.

Mike.